Sorbitan fatty acid esters have wide spread utility in many areas as an emulsifying agent in the formation of water-in-oil and oil-in-water emulsions. They are readily available commercially as SPAN.RTM. emulsifying agents and ALKAMULS.RTM. sorbitan esters.
Sorbitan esters can be manufactured by processes described in U.S. Pat. No. 2,322,820. Generally, sorbitol and a fatty acid, or a combination of fatty acids are reacted at a temperature greater than about 200.degree. C. under a flow of inert gas, in the presence of an acidic or basic catalyst, to produce sorbitan fatty acid esters. A combination of mono-, di-, tri-, and tetra-esters of sorbitan as well as impurities such as polyols formed by the self-condensation of sorbitan molecules, unreacted sorbitans and isosorbides are produced from this process. These impurities are also present in the commercial sorbitan esters.
It has been found that these polyol impurities tend to form undesirable sludge during emulsifying processes. Therefore, it is desirable to remove these impurities from the sorbitan fatty acid esters in order to avoid the formation of sludge.
It is therefore an object of the present invention to provide a process to purify sorbitan esters containing polyol impurities.